From German Pat. No. DE-AS 2621302 there is known a compensated measurement transducer for measuring a first current generating a first magnetic field of a predetermined direction and flowing in a first circuit, including a first conductor, by generating a second current substantially similar to the first current in a second circuit, and obtaining the value of the second current. The second circuit includes a compensating current conductor generating a second magnetic field having a direction opposite to the predetermined direction, so as to compensate the first magnetic field, a magnetic transducer having a first and second magnetic field applied thereto, and an amplifier connected to the output of the magnetic transducer and coupled to the compensating current. The conductor and compensating current conductor are primary and secondary windings of the transformer, respectively, and are wound around a magnetic core. The magnetic transducer is a Hall-effect transducer, which is disposed in the air gap of the magnetic core.
In a compensated measurement transducer employing a Hall-effect transducer it is not possible to omit the magnetic core as the magnetic fields, which are to be measured, must be applied at right angles to the main plane of the plate-shaped Hall-effect transducer, which is only possible by means of a magnetic core at an adequate efficiency, in view of the low sensitivity of the Hall-effect transducer.
From the IEEE Transaction on magnetics, November 1976, pages 813 to 815, there is also known a Wheatstone bridge including magnetoresistive thin films for measurement of a magnetic field generated by a current. From German Pat. No. DE-AS 2344508 it is also known to measure a magnetic field by means of a thin ferromagnetic film and to compensate the magnetic field to be measured by means of a compensating coil generating a controllable and known magnetic field; in this application, however, the magnetoresistive effect of the thin films are not made use of, but only an induced electrical signal is analyzed. The equivalent U.S. patent is No. 3,931,572.
From U.S. Pat. No. 3,820,089 there is known a magnetoresistive bridge for detection of magnetic bubbles.
From U.S. Pat. No. 3,546,579 there is known a magnetometer utilizing a thin-film bridge, in which the thin films are magnetized along their easy axes.
A compensated measurement transducer of the initially described type employing a Hall-effect sensor in the air gap of the magnetic core is also known from U.S. Pat. No. 3,649,912.